Phosphotriesterase Homology Protein (PHP) is a 33 kDa protein found in E. coli which bears 28% identity to phosphotriesterase. There is no currently known function. Since crystal structures have been solved for both holoenzymes, a current approach to determining functionality is to overlay the two proteins and determine differences in the active site of phosphotriesterase and the putative active site of PHP (based on the alignment). From here, I can determine particular residues that can be mutagenized and mutagenize "in silico" as well, so that I can use graphics to see the structural effects of each mutant.